Steel Rectangular Tube 70X30

Updated: 2026-09-16

Overview

Steel Rectangular Tube 70X30 is a cold-formed hollow structural section (HSS) with standardized external dimensions of 70mm width and 30mm height. Produced through either welded or seamless manufacturing processes, these tubes offer superior mechanical properties compared to solid bars of equivalent weight. The rectangular profile provides excellent resistance to bending in both major axes, making it particularly suitable for structural applications where bi-directional load distribution is required. As a standardized industrial product, these tubes are manufactured according to international standards such as ASTM A500, EN 10219, or JIS G3463, ensuring consistent quality and dimensional accuracy. The 70x30mm size represents a mid-range profile that balances structural capacity with material efficiency, commonly stocked by steel service centers for immediate availability.

Structure and Working Principle

The rectangular tube's structural efficiency derives from its geometric distribution of material away from the neutral axis, creating high moment of inertia values in both principal directions. The closed section provides superior torsional resistance compared to open profiles like channels or angles. Wall thickness (typically ranging from 1.5mm to 5mm) directly determines the tube's load-bearing capacity and stiffness characteristics. From an engineering perspective, these tubes function as either compression members (columns), flexural members (beams), or combined axial-flexural components in structural systems. The hollow interior allows for convenient routing of utilities (wires, pipes) in architectural applications, while the flat surfaces facilitate clean connections and mounting of secondary components in machinery designs.

Key Features

The 70x30mm steel rectangular tube offers several technical advantages: dimensional stability during fabrication due to its symmetrical geometry, excellent weldability with common arc welding processes, and compatibility with standard metal finishing techniques. The profile's flat surfaces simplify connection detailing and component mounting compared to round tubes. Material options include mild carbon steel (Q235, A36) for general applications and high-strength low-alloy steel (Q345, A572) for demanding structural uses. Surface treatments like hot-dip galvanizing (typical coating weight of 275g/m²) significantly enhance corrosion resistance for outdoor applications. The tubes exhibit consistent mechanical properties with typical yield strengths ranging from 235MPa to 345MPa depending on material grade.

Application Areas

Construction sector applications dominate usage, including purlins, truss chords, and framing members in commercial buildings. In industrial settings, these tubes serve as machine frames, conveyor supports, and safety guarding structures. The automotive and transportation industries utilize them for trailer chassis components and cargo handling equipment. Architectural applications exploit both structural and aesthetic qualities, visible in modern façade systems, canopy supports, and interior design elements. Agricultural equipment manufacturers value these tubes for implement frames and livestock handling systems due to their durability and ease of modification. The 70x30 size is particularly favored for medium-span applications (3-6m) where its proportions optimize material usage.

Maintenance and Precautions

Regular inspection for corrosion is essential, especially in humid or chemically aggressive environments. Surface damage to protective coatings should be promptly repaired using appropriate touch-up paints or zinc-rich compounds. For structural applications, periodic checks for deformation or cracking at connection points are recommended. During installation, proper alignment techniques must be employed to prevent induced stresses from forced fit-up. Cutting should be performed with methods that minimize heat-affected zones (cold sawing preferred over torch cutting). When welding, follow preheat and interpass temperature guidelines for the specific steel grade to avoid hydrogen-induced cracking.

B2B Procurement Guide

Industrial buyers should specify: material standard (e.g., ASTM A500 Grade C), wall thickness tolerance (typically ±10%), straightness requirements, and surface condition (mill scale, pickled, or pre-primed). Quantities are normally purchased by weight (metric tons), with single-piece lengths commonly ranging from 6m to 12m. Lead times vary from stock availability (1-3 days) for common grades to several weeks for specialized materials or treatments. Minimum order quantities (MOQs) typically start at 1 ton, with price breaks at 5-ton increments. For large projects, consider ordering pre-cut and drilled components to reduce fabrication costs. Always request mill test certificates (MTCs) for critical structural applications.